Pharmacokinetic service is about using drug serum concentrations, Pharmacokinetics, and pharmacodynamics to individualize and optimize patient response to drug therapy. It is also about understanding the merits, limitations and applications of using serum drug concentrations in quantitative decision making. The aims of this paper are that covers in detail the commonly monitored using serum drug concentrations as adjuncts to decision making, how drugs are monitored, and the template for characterizing outcomes of TDM from both system-related and patient-centered viewpoints.